台风榴莲(2001)在季风槽中生成的机制探讨

An investigation of the genesis of typhoon Durian(2001) from a monsoon trough.

利用NCEP 1°×1°分析资料、TMI海温资料、卫星云图资料对季风槽中南海台风榴莲(2001)生成机制进行了分析,揭示了大尺度环境流场、温暖洋面、中尺度对流活动对热带气旋(TC)生成的控制作用。结果表明,水平风速垂直切变的演变在一定程度上指示着TC在暖湿洋面上生成的时间,水平风速垂直切变由强向弱转变,在TC发生前18小时迅速减小到10 m/s,随后在10 m/s以下维持少变,垂直切变的变化主要反映了对流层高层环流形势的演变;在对流层中低层,季风槽的形成和加强对TC的生成有重要作用,由于热带温暖洋面作用,季风槽首先表现出有利于单体对流和带状对流发生发展的条件性对流不稳定特征,随着季风槽的加强,季风槽进一步表现出有利于中尺度扰动发生发展的正压不稳定特征;季风槽槽线南侧的低空急流的经向分布很宽广,由105°E越赤道气流和中南半岛偏西气流(其源头是索马里越赤道低空急流)汇合而成,急流的加强活动具有经向差异,由于边界层高θ_e空气辐合抬升产生两条经向距离约300 km的显著带状对流云系,槽线南侧风速分布的经向差异导致两条带状云系发生追赶,并逐步在季风槽底部槽线附近合并加强为MCC,进而导致中尺度涡旋(MCV)的产生并最终发展成为TC。分析结果还表明,为深对流供应丰富对流有效位能的主要是来自台风发生区域本地南海暖洋面的地面热通量,南海暖洋面对TC生成有重要贡献。台风榴莲的生成是一个多尺度相互作用过程,主要包括涡旋对流热塔、与带状对流云系伴随的涡度带的升尺度,涡度带合并成长为MCV,以及大尺度条件对TC在季风槽中生成的时间及地点的控制作用等。

The genesis of Typhoon Durian （2001） from a monsoon trough over the South China Sea is investigated using the NCEP analysis, the TMI sea surface temperature （SS T） data and satellite imageries. The results reveal the important roles of large rscale flows, warm SSTs, and convectively generated vortices in determining th e TC genesis. Of importance is the timing of the TC genesis. Durian appeared as the vertical wind shear decreased to a critical value of 10 m/s as a result of changing largerscale flow pattern in the upper troposphere. It is shown that t he monsoon trough was conditionally unstable to deep convection and barotropical ly unstable to mesoscale disturbances. Low-level jets associated with a cross -equatorial flow and a westerly flow from IndoChina Peninsula provided favo rable lifting-？e air in the boundary layer for the development of two major convective bands to the south of the trough axis. As the two convective bands, spaced meridionally about 300 km apart, moved toward the trough axis, the associated vortices were merged into the monsoon trough, leading to the generation of an MCV and its subsequent growth to typhoon intensity. It is also shown that surface heat fluxes from the underlying warm ocean played an important role in feeding convective available potential energy to deep convection during the TC genesis. We conclude that the genesis of Typhoon Durian involved multi-scale processes, including vortical hot towers, upscale growth to vorticity bands, their merging to an MCV, and the large-scale control of the timing and location within the monsoon trough.